Old account authorization fail

I have songs downloaded from an old iTunes account. They no longer play. I've authorized them with the old account information--no dice. I've tried removing the "/users/Shared/SC Info" folder and rebooting per Apple's support pages--no dice. When I authorize under the old account, it says I've authorized the computer, but then refuses to play the songs--not the case for de-authorized and re-authorized songs under my current account. This is getting extremely annoying. (What I'd really like to do is get every thing under the same account!)

Help & TIA!!